1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a method for manufacturing the electrophotographic photosensitive member, a process cartridge, and an electrophotographic apparatus.
2. Description of the Related Art
Electrophotographic photosensitive members used in electrophotographic apparatuses, such as a copying machine and a laser beam printer, need to have a sensitivity adequate for light to which images are exposed. It is known that azo pigments and phthalocyanine pigments used as charge-transporting substances exhibit high sensitivity to light in a broad wavelength range.
In recent years, images of high quality, such as high-quality color images, have been demanded. Half-tone images, such as a picture, and solid images are widely used, and the quality of such images has been enhanced year by year. In recent years, tolerance for a phenomenon called “positive ghost image” has been significantly narrowed; in the phenomenon, the density of the limited part of a half-tone image corresponding to the light-irradiated part of an electrophotographic photosensitive member becomes strong at the subsequent rotation of the electrophotographic photosensitive member in formation of one image. It is believed that such a ghost image is generated for the following reason: holes which are a type of carriers (electrons and holes) generated from a charge-generating substance are injected into a charge-transporting layer, and then electrons are likely to remain in the charge-generating layer to cause a transfer memory.
Japanese Patent Laid-Open No. 2006-72304 discloses a technique in which a charge-generating layer contains a composite of a phthalocyanine pigment and an organic electron acceptor compound to reduce generation of defective images such as a ghost image. Japanese Patent Laid-Open No. 2008-15532 discloses a technique in which a charge-generating layer contains a pigment-sensitizing dopant having electron acceptor molecules to reduce generation of defective images such as a ghost image.
The inventors, however, have conducted studies and found that the techniques disclosed in Japanese Patent Laid-Open Nos. 2006-72304 and 2008-15532 cause an increase in the particle size in a coating liquid for the charge-generating layer and are thus inadequate for enabling reduction in both a ghost image and a black-spot image in some cases.